Gas analysis apparatus



Aug. ll, 1931. T. R. HARRISON 1,818,619

GAS ANALYSIS APPARATUS Filed Aug. 19, 1926 2 Sheets-*Sheet l fab au T a a me BY MA @MM ATTORNEY Aug. vll, 1931. v T. R. HARRISON 1,818,619A

l GAS ANALYSIS APPARATUS Filed Aug. 19, 1926 2 Sheets-Sheet 2 KI 2 BY www ATTORNEY Patented Aug. `11, l,19:1

THOMAS R. HARRISON,

INSTRUMENT COMPANY, 0F PHILADELPHIA, PENNSYLVANIA,

PENNSYI. VANIA or rmLsnELrnirENNsYLvANIA. AssIGNon 'ro 'rmi-Brown conciernen or' u eas ANALYIISAPPABATUS:

The general object of my presentfiiiven-"-j tion is to provide improvements in appara? tus for ydetermining the composition o f a gas b measuring or comparing electrical quantities which are' dependent on thether-v mal conductivity 'of the gas, vwhich depends in turn upon the composition ofthe gas.- My improved apparatus is like'that heretofl fore known for the purpose in thatfit comprises a structure or housing containing cells inl each of which is located a resistor, the

resistance of whichvariesgwith the temperaf` ture of the resistor, and in that lthe tempera-J.v

ture of each such resister depends uponA the heatimT effect of'an electric current passing througi it4 and upon the ycoolin effect of a lody of gas filling the-cell'fian conductingI eat rounded by the gas to' be analyzed and at least one other cell, the resistor in which is surrounded by a standardor com arison gas, which frequently is air, so that t e composition ofthe gas to be analyzed is determined by a comparison of the resistance values of the different resistors which are ordinarily connected. into a Wheatstone bridge.

My present invention comprises improvements in the cell containingstructures which facilitate the proper construction 'of lsuch structures at a relatively low cost of production. The invention also comprises improvements in the mode of mounting the resistors in the' gas cellswhich are desirable from a mechanical standpoint, vand which permit of a novel adjustment of the resistors to vary the temperatures attained b them under given conditions, lthereby faci itating the calibration of the apparatus. The improved cell containin vstructure is characterized particularly the fact that the cellwalls are so formed as to resist the corrosive action of gases'having a corrosive action on metals such as iron or brass heretofore employed, and so as to prevent objectionable gas diffusion through the cell wall pores such as sometimesoccurs when the 'cell walls are formed of iron or brass,

from the heated resistorz tothe sur l'-structure, rounding wall of the cell.` UsuallyI such V` apparatus comprises at least one cell in,

-which the corresponding resistor is sur.

.scribed preferred embodiments of the in- Y ss The invention is further-characterized by i "the provisions'f'or regulating theftemperature and moisture content of the ga'ses being compared, andl in particular by the f Apre- ;visions made for having the gases compared practically, saturated with' water vaporA while,` at the same time avoiding the presence of entrained moisture in the gases Howing through the comparison cells.

In a preferred form of construction, the

lnecessary means `for preliminarily cooling the gases and condensing excess moisture and iltering the gases to clean ture with. the comparison cells, instead of being separate lfrom the comparison cell as has heretofore been the practice. By this combination the construction of gas analysis apparatus is cheapened, the apparatus is made more compact, and the maintenance of practically the same temperature and humidity conditions for the gases compared is facilitated.

The various features .of novelty which with articularity in the claims annexed to and orming a part of this specification. For a better understanding `of the invention, however, its advantages andspecific objects attained by it, reference should be had to the accompanying matter in which I have illustrated an devention.

Of the drawings:

them, preparatory `to their admission to the comparison cells" are combined in a unitary mechanical struc simplified and drawings and descri tive,

Fig. 1 is a plan view of a gas analysis I device;

Fig. 2 is a section on the broken line 2-2 of,F1g. 1;

Fig. 3 is a section on the line 3--3 of Fig.'

Fig. 4 is a partial section on the line 4--4 of Fig. 1;

Fig. 5 is a section on the line 5-5 of ig. 6 is a diagrammatic representation of ,apparatus for ymeasurlng the CO and CO,

content of l'flue gases;

Fig. 7 is a section .on the line 7--7 yof Fig.

V'ns 'characterize-my invention are pointed out 8 illustrating a modified construction; n

Fig. 8 is a section on the line 8-8 of Fig. 7 and Fig. 9 is a diagram of circuit connections which may he employed with the apparatusshown in Fig. 6.'

In Fig. 6 I have diagrammatically illustratedthe use of various features of the present invention in apparatus comprising a sampling tube A adapted to be inserted into a furnace chamber or flue from which :sis

`filling a cavity D furnace gases are to be Withdrawn for analysis. portion of the gases thus Withdrawn from the sampling tube `A passes through a pipe B to the gas inlet of a device C containing provisions for cooling and cleaning the gases, and containing `compari- CO2 content gases entering the device C, pass from the latter through a pipe B to a device CA containing comparison cells for determining the CO content of the gases withdrawn through the sampling tube A. The'device CA also contains provisions for -cooling and cleaning gas coming from the sampling tube A'through the pipe B3. Interposed in the pipe B2 between the sampling tube and device CA, is a furnace F containing copper oxide or an analogous oxidizing agent forfconverting the CO content of the gases passing through the furnace into CO2. The gases entering the device CA through the pipes B and B2, are Withdrawn from the device CA throu h a pipe B3 running to the inlet of an aspirator Gin which Water supplied under pressure through the pipe L3 creates thel draft/f for causing the above described flow through theapparatus.

I G represents the outlet from the aspirator through which the air, gas and aspirating water are discharged.

As shown, the aspirating Water is supplied from a pipe L and is utilized in cooling the gases in the devices C and CA. For this purpose branch L runs from the supply pipe L to the water inlet of each of the devices C and CA. The water outlet of each of the devices C and CA is connected by a corresponding pipe L2 to the pipe L3.

The device C comprises a metallic body D and a metallic` cell block E extending into the upper end of, and nearly, but not quite in the member D. The cell block E is form/edwith a lateral flange or head E at its upper end resting against, and bolted to the top of the member D. The body D and cell block E may each be a one-piece aluminum casting. The body isformed with vertical water channels D2 in communication at their upper ends and connected at their lower ends, one' to the inlet pipe L', and the other to the outlet pipe L2 pertaining tothe device.

The gas supplied to the device C b the pipe B` passes successively up, then own,

- D5, th

Vis subjected to a cleaning action in each .the cell block head E ,leads from the bottom of the cavity cells e and ea, are

and then up, through connected vertical passages D3, D4, and D5, formed in the body D, to a gas inlet passage E4 formed in the head or lateral iiange E of the cell block E. In fiowin'g through the passages D3, D, and e gas is cooled and cleaned. llllhe gas passage, but the gas is cooled, wholly or mainly, in the passage D3 which is in relatively good heat transfer relation with the Water passages D3, and serves in lieu of the separate condenser heretofore employed to condense excess moisture in the iiue gases. To clean the gas, as well as to screen out entrained Water of condensation, suitable screening or filter` material is placed in the passages, such as glass beads d, glass wool ci', steel Wool d2, absorbent cotton d3, and an alundum filter tube d4. The latter as shown is carried by a plug E2 threaded through an opening in and formed with passages through Which the interior of the tube @Z4 communicates with the channel E4. DG is a window through which the interior of the passage D5 may be inspected.

Formed in the body of the cell block E are two vertical resistance containing cells e, two vertical resistance containing cells ea, and a vertical chamber e. rlhe cells e and ca and chamber e may be holes formed by a drill entering the cell block at its upper end.

he open upper ends of each of the cells e and ea are closed by a plug M and threaded gland M securing the plug in place; and a pilug m closes the upper end of the chamber e The cells e communicate at their upper ends with, and receive gas from the channel E?, and discharge the gas through restricted outlets at their lower ends into the temperature equalizing space within the cavity D surrounding and beneath the cell block. This space also receives some gas at itsu per end directly from the channel 4 through parts E3. The gas outlet pipe B D. The cells ea communicate with the chamber e at their upper ends and with the latter are sealed and contain air or other standard or comparison gas. The chamber e contains a humidity regulating agent which might be a drying agent, but preferably is' water, Wet cotton or some other'` humidifying agent.

The plugs M closing the upper ends of the formed of insulating material and support the cell resistance terminals O and P. As shown, each plug M is formed with a central passage for a barlike terminal O which extends through the plug, and secured in anyl desired axial adjustment thereinby a set screw O. The terminal bar O in each cell e has its lower end secured to the u per end of a corresponding resistance R, which is in the form of a helix and has its lower end connected to a terminal .P

.carries a spider P of centering th Alower end of the resistance 1n shown as a metal rod extending through and the corresponding cell without closing the latter. The terminal bars O extendinginto the upper ends oithe cells ea have their lower ends connectedf'to theupper ends of body.

l the cell block E. The' gas wi helical resistances r which have their lowerends supported by arms P and spiders P just as do the resistances R.

In the preferred construction illustrated, a so-called'Wheatstonebridge balancing resistance in the form of a slide wire S, is mounted on the periphery Vof a semicylindrical block ofbakelite or other insulating ma.-v

terial S securedv to the head o-the member E. vThe block S 'has journalled in it a shaitS2 carrying a brush S3 which bears against the resistance S at a point depending on the angular position of the shaft-S?. The block S may also serve as a sup ort for binding posts or the like through w ich theresistors R and 1- are connected to the terminall leads or conductors of the device C. which, as shown, are incor orated in a cable Q advantageously exten ing through f a Vertical channel D7 formed in the housing The device CA may be identical in construction with the device C except that as shown in the device CA the chamber e does not serve as a drying chamber but as a' means'for connecting the gas pipe B to the tops of the cells ea, and that the latter are connected at their lowerends by restricted ports to the space in the cavity D beneath t its original CO content converted into CO2 in the furnace F, conveyed by the pipe B2 to the device CA, after passing through the cooling and cleaning passage of the device CA enters the cells e of thc latter. rIhe gas outlet pipe Bil leads from the bottom of thecavity D( of the device CA. v

In Fig. 9 I have illustrated diagrammati- -cally one 'form of circuit arrangements by which the resistances R and 7' of the devices C and CA may advantageously be employed vin connection witha single meter K to eX- hibit in a readily rcomparable manner the CO, and CO2 contents ofthe ases drawn into the apparatus through t e sampling tube A. In Fig. 9 the two resistances R of the `device C- form opposing arms of a Wheatstone bridge,'0 f which the gather 4two arms are formedby the resistancesr. y The bridge is energized by a source of current as a battery U, conductors 1 and -2 connectin the battery to op osing junction points o the bridge. As y own, the conductor 2 is connecte tditlie 'slide vwire brush Sa which forms lone ljunctionof the brid e, the slide wire resistance S connecting adjacent ends which 'the strength of the bridge current-can 'be regulated. The other two junction points of the bridgel ofthe device C are connected by? conductors 3fand 4 to terminals of 4a switch ll. Y

The resistors R and r of the device CA are connected into a Wheatstone bridge arranged energized and connected to terminals ,of the switch I- as is the bridge of the device C. The connections to the bridge. of the device CA comprise conductors 10, 20,80, and 40 corresponding tothe conductorsl, 2, 3, and 4, respectively, associated with the bridge of the device C.. The switch' I is intended for manual or automatic lactuation to separately connect thetwo bridges in regular alternation to the winding of an indicating Aor recording galvanometer K. Advantageously, though not necessarily, the pointer K"` ofthe meter K swings over the meter scale K2. in one direction from the zero point K3. of the scale when connected by conductors 3 and 4to the bridge C Dto thereby indicate theCO2 content of the gas, and swings in the opposite direction from the zero point to indicatev the CO content of the gas when the meter is connected through conductors 30 and 40 to the bridge of the device CA.

With the meter poi te'i` opposite directions from the zero point of the instrument to indicate CO2 and CO contents, respectively, the zero point is preferably located at one side of the center of the scale so that the instrument will give a wider ran e of scale readings when measuring CO2 t en when measuring CO, which is desirable in view of the fact that the CO2 variations will normally require a .wider range of movement of the pointer for their proper indication than will the CO measurements. With the arrangement' for this purpose shown in Fig. 9, the portion of the scale K2 at the right of the zero point K? will ordinarily be graduated in CO percentage units,

while the portion of the scale at the left of the Azero point will be graduated in CC2 percentage units. When, as will be usually the case, the meter K is arecording meter, the location of the CO and CO2 records at thus swinging inl opposite sides of the zero line makes it unthe c as the electrical quantities measured differ scale, the meter K and the switch I of known type.

As those skilled in the art will understand, when the instrument K is connected by the conductors 3 and 4 to the Wheat- Stonebridge of the device C and the bridge is properly energized and calibrated so that the pointer K will stand at the zero point when the resistors R and 1' are at the same temperature, the lower thermal conductivity of the CO2 content of the gases in the cells e as compared with the air in the cells ea, will cause the resistors R to be hotter, and in consequence to have higher resistances than the resistors 'fr by an amount which is dependent on the-` amount of CO2 in the gases passing through the cells e. Similarly, when the bridge of the device CA is connected to the winding of the meter K, the instrument pointer K will be defiected more, or less according to the excess in the CO2 content of the gases passing through the cells ea, over the` CO2 content of gases'passing through the cells e, the CO in the gases passing through the cells e having about the same thermal conductivity as air and other constituents, aside from CO2, of ordinary furnace gases. It will be understood that in the VVheatstone bridges shown in Fig. 9, the same general operation would follow, if one resistance R- and onel resistance r of each bridge were replaced by fixed resistance arms. The use of two resistances R and two resistances r, as shown, makes it unnecessary t'o provide fixed bridge reslstance arms, while adding to the sensitiveness and rangeof the bridge indications.

The apparatus disclosed possesses numerous important practical advantages. An advantage of the' cell block and resistor mounting structure illustrated is the ready feasibility-of incorporating more than one pair of comparison cells in a single metallic lock or body, since each cell block can be made large enough to incorporate as many cells as may be required and the different resistors are insulated from the cell block. In

may be v practice, the electrical determination of gas composition, based on the thermal conduc=` tivity of the gas, re uires effects due to the di tivities .of the test gas a comparison of erent thermal conducand of a standard gas so slightly as to make absolute measurements based on the test gas alone uncertain and unreliable.

-The accuracy of comparison cell measurements depends, of course, upon thepractical elimination of all temperature differences between the cells compared exce t the differences which result from thel di erent thlelrmal conductivities of the gases in the ce s.

Furthermore, it is highly desirable to eliminate appreciable inequalities in the humidity or waterv vapor content ofthe gases compared, since such inequalities tend directly to errors Iin the measurements made, the possible error being greater at higher temperature. With the device C described,

the flue or other test gas is `reduced to a temperature definitely related to the temperature of the cell block.l In passing through the cleaning and coolingpasages D3, D4, and D5, the test gas is ordinarily cooled to a few degrees below the temperature of the cell block, since the latter receives heat from the resistances e and ea, and the dissipation of this heat is too slow to prevent the cell block from being a few degrees warmer than the housing body. The temperature equali- Zation of the cell block and body is impeded by thejjoint resistance to heat transfer from the portion of the cell block head E clamped against thetop of the housing body D, part-icularly as a non-metallic gasket is ordinarily Iinterposed to or below its saturation temperature. The filter provisions prevent entrained moisture from being carried into the cells, and even if some minute quantity of free moisture did,

enter the cells with the test gas, the increased temperature imparted to the gas in the cell block insures the evaporation of this moisture, as with its increased temperature the gas is then slightly under-saturated. In consequence the cell walls are kept clean, and the diiference between the humidity of the test gas and of the saturated air orv other standard gas sealed in the cells ew and chamber -c is so slight as to be inconsequential from a practical standpoint. The method of compensating for the humidity of a test gas lby maintaining it and the standard gas each in a practically saturated condition has not heretofore been accurate in ractical gas analysis apparatus, because o the inability in such prior apparatus to maintain the approximately uniform temperature conditions secured with the present invention. f

It will be apparent that the gas comparison devices C and CA disclosed tend to equalize the temperature of the gases compared, by reason of the formatlon of the cells in a unitary metallic cell block, and the enclosure of the latter in a unitary metallic housing body, so that the' use of the cooling water in the always essential. .The use' of cooling water as described, however, prevents-the test gas from entering the comparison cells vniuch between the head and passages D? is notlv-.

under-saturated, as it mlght if the gas were v creases rapidly as the gas rises in temperathemeasurements obtained do notdirectly depend upon the celly block temperature, .1t

is generally desirable to have the cell block temperature comparatively low because the water vapor content of a saturated gas inture above ordinary atmospheric temperatures, and the higher the saturation moisture or it may be periodically removed byopen ing the passages D3, D4L land D5 lat their lower ends las is readily possible with the construction illustrated. The quantity of condensate collecting in the apparatus in any one` period of use is ordinarily quite small,

and all orpractically all of this -condensate will collect in the lower end of the chamber D3. In practice I consider it desirable in some cases to maintain a body of oondensate iii the lower end of the passage D3, and to place lwater in the bottom of that channel when the apparatus is initially put into operation, so that the entering gas will bubble 4throughthe water. This notoiily neutralizes the effect of transitory variations in the temperature of the entering gas lbut is primarily important because it insures `full saturation at all times of the gas flowing upward through the channel D3.

In the'` comparison cell device OA, the gas passing to the chamber e and cells ew through the pipe B', will ordinarily reach the cells at practically the temperature at which it leaves the device C, and hence at about ther same tem erature at which i-the gas coming to the evice "CA througlrfithe .pipe 1?2 enters the cells e of that device. In consequence it is not ordinarily necessary to pass the gas supplied by the pipe B through coolin channels'A in the bod D of the device CA, t ough this mayv readily be provided for whenever necessary or desirable, as it involves nothing more than the formation of an extra gas assage or passages inthe body D, and in t e head of the cell block E of the device CA. l

The mechanical structure 'of the devices I C and CA is obviously simple and desirable for reasons already explained. Furthermore, the fact that the gas cells are formed iii a cell'block separable from the body'ofl each comparison cell structure, makes it ossible to do rough mounting work, inclu ing `the attachment of all pi e connections to each such body before t e corresponding cell block is put into place, and thus eliminates a source of injury by mechanical shock to the resistance filaments which are rela- "tively delicate and easy to injure.

opposite ends to rigid conductors O both mounted in the saine insulation plug M in which the conductor O is axially adjustable, is an important characteristicof the apparatus since this permits of a variation of the temperature and thereby the resistance attained by the resistor under any given conditions of operation. lThis follows from vthe fact that the rate at which the resistor dissipates heat is increased, other things being equal, by spreading the resistor convolutions -*farther apart, and is diminished by bringing them closer together.

lThis feature of the invention makes it reade The resistor arrangement disclosed offers aneasy method of obtaining a condition which has heretofore been impracticable obtain; namely, of having the bridge in f bala-nce when the test gas cells e contain as of normal or average composition, as or example furnace gases containing 14% of CO2, while the comparison cells ea contain a convenient gas such as air. "Inthis case the convolutions of resistors R ma be spaced farther apart, or be wound with a larger diameter, to increase the cooling effeet of the gas of relatively vlow thermal conductivity contained in cells e. distance between the resistor convolutions may be adjusted while the apparatus is in, or in condition for operation, the necessar adjustment may readily be made with eac individual "instrument, which is evidently impossible if different sizes of'resistor wires are used for resistors R and fr, or if different diameters are used for cells e and ea as have heretofore been suggested. The method just described is superior also to the method of balancing the bridge when usingv unlike gases in cells e and ea by adjustment of the slide wire S, because w en the slide wire is .placed ina position other than that which balances the bridge when the resistors Since the ioo iio

are unheated, the meter readingwill change v 'when the bridge current varies Aslightly when When balancedv normal gas is in cells'e.

with normal gas no error is produced at this reading by the galvanometer temperature coefficient. l

The disclosed mode vof mounting the resistors in the cell blocks avoids all necessity for grounding the resistors to the cell block, and thus permits two or more resisable use with the cell corrosion troubles.l

water inlet and outlet pipes tors R and two or more resistors r to be mounted in a single cell bloclr, andto be connected in a single Wheatstone bridge as shown in Fig. 9, which is not possible when one end of each resistor is grounded by contact with the cell block, as has heretofore been the usual practice.

The formation of the cell blocks E of cast aluminum is of advantage because cast aluminum is not corroded by gases which. will corrode iron or brass, which have heretofore ordinarily been employed, and in many cases have been gold-plated to avoid Where trouble is anticipated from gas diffusion through the pores of the aluminum, the cell block may be dipped in molten cannauba wax, or beeswaX, or varnish, and the Wax or varnish bath then subjected first to vacuum and then to pressure, whereby the cell block pores are filled. The wax hardens' as soon as the casting4 is removed and cooled, and the varnish im regnated casting may be airdried or baked to oxidize and harden the varnish. Treated with either material, the cell block is gas tight, and the cell walls and channels are coated with a material highly resistant to the corrosive action of gases in contact therewith.

Instead of makingthe cell walls of aluminum, they may well be made in some cases of lead, as in the construction shown in Figs. 7 and 8, wherein the cell block EA, while it may otherwise be identical in form with the cell block previously described, has'its body portion composed of a shell E10 cast integral with the head of the cell block, and surroundin a lead core E11 cast in place therein. Tie cells e and ea, and the chamber e', may be drilled in the core E, cr may be formed by the use of suitable core patterns when the lead core EL is cast. Thel use of lead as a cell wall material is advantageous because lead'is not suiiicientl porous to permit objectionable gas didusion through the cell walls, and because lead is not corroded b sulphur compounds or other constituents o furnace gases which have a corrosive action on. such metals asA iron, coppar or brass. ,Corrosion of a cell wall is to avoided if for no other reason than because it modifies the rate of heat transfer between the cell wall and the enclosed resistor.

The cell block EA may be identical in contour and in the arrangement of its cells, chambers and .passa es with the cell block 1t is a a ted for interchangelock E in the same body D. In Fi 7 and 8, how does not -include gas filtering provisions, but does include a water jacket yspace D1", which surrounds the cell block cavity D', and to which cooling L' and L2 are E so that that housin connected. The lhousing body DA is formed with cooling gas passages D11 and D12, through one of which gas may be passed to the cells e, while the other is sealed or is used to pass gas to the cells ea of the cell block EA, as conditions make desirable.

Certain novel features of the inventiondisclosed but not claimed herein are claimed in my copending application Serial No. 68,650, filed November l2, 1925, of which in certain respects this application is to be re.- garded as a continuation.

lVhile in accordance with the provisions of the statutes I have illustrated and described the best form of embodiment of my invention now known to me, it will be apparent to those `skilled in the art that changes may be made inthe form of the apparatus disclosed without departing from the spirit of my invention as set forth in the appended claims and that in some cases certaln features of my invention may be used toadvantage without a corresponding use of other features.

Having now described my invention, what I claim as new and desire,to secure by Letters Patent is:

1. Gas analysis-apparatusjcomprising gas cells and electrical resistance members therein, and an enclosing metallic structure formed with a gas cleaning and cooling space, gas cleaning provisions therein and connections or passing gas through said space into one of said cell f 2. Gas analysis apparatus comprising a cell block formed with gas cells, gas heating resistances in said cells and a metallic structure surrounding said cell blockJ and in relatively poor heat conductive relation therewith, said structure being formed with a gas passage communicating with, and supplyin gas to one of said cells. y

3. as analysis apparatus comprising a cell block formed with gas cells, gas heatlng resistances in said cells, and a metallic structure surrounding said cell block and in relatively poor heat conductive relation with the latter, said structure being Iformed with a gas passage communicating with, and supu plying gas to, one of said cells, and with a water cooling passage. y

4. In determining the thermal conductivity of a gas, the method which consists in cooling the gas toa temperature as lons -its saturation temperature, removing entrained moisture,slightly increasing the temperature of the gas and then comparin the thermal conductivity of the gas wit that ofa saturated gas at approximately the same temperature. c

5. A comparison cell device for measuring the thermal conductivity of a gas which comprises gas cells, anl enclosing metallic structure :formed withy gas cooling and clean- EEO ing passages, and gas cleaning provisions therein.

6. Aplgmratus for furnace gas analysis comprisingr cells a'nd resistors for determining the C()2 content of the gas, 'cells and v resistors for determining the CO content 'of the gas, a meter, said meter vcomprising a scale having a zero point and a pointer adapted to swing in either direction from said zero point and means for connecting it alternately to the resistors for C02 determination and to the resistors for CO determination, said means being so relatively' arranged that the pointer will swing in one direction from said zero point when connected to one set of resistors and will swing in the opposite direction from said zero point when Aconnected to the other set of said resistors.

7. In determining the thermal conductivity of a gas, the method which consists in initially adding moisture to the gas as required to saturate the latter, then removing entrained moisture from the gas, and slightly increasing the temperature of the gas, and then comparing the thermal conductivity of the gas with that of a saturated gas at approximately the same temperature.

8.V In apparatus lfor determining the thermal conductivity of a gas', the combination of a cell structure comprising a body member of aluminum formed with a gas receiving cell chamber, aresistor therein formed of material varying in electrical conductivity as its temperature varies, means for passing an electric heating current through said resistor, and -means responsive to the voltage drop in said resistor.

9. Apparatus for gas analysis com rising cells and resistors for determinin t e002 content of the gas, cells andv resistors for determining the CO content. of the. gas, a meter, and means for connectin it alternately to the resistors for CO2 etermination and to the-resistors for C() determination.

- each of said cells,

comprising two test cells and afiresistor in means for passing some series through the of the 'gas to be testedin test cell of the first mentioned device and through one of lthe test cells of the second` mentioned device, means for passing some of the gas to be tested 'in series through said CO converting means and through the second test cell of said second mentioned device, an electric meter, andv means for connecting it alternately to the resistors of the irst mentioned device and to theresistors of the second mentioned device.

12. Apparatus for gas analysis comprising in combination a thermal conductivity device comprising comparison cells yand resistors therein, a second thermal conductivity device comprising comparison cells and resistors therein, means for converting the CO content of gas into CO2, means for passing gas through the last mentioned means and thence through one'of the cells of said second device, means for passin gas through a cell'of thegfirst device and t ence through a second cell in the second device, means associated with each of said devices for conditioning gas entering the cells there-l of, and electrical measuring means associated withvsaid resistors.

Signed at Philadelphia, in the county of Philadelphia, and State of Pennsylvania, this 17th day of rlst, A. D. 1926.

' THO S R. HARRISON.

10. In. apparatus for gas analysis, the

lcombination of a 'thermal conductivity device comprising cells and resistors for creating an electrical force which is a measureof the initial' CO2 content of agas, means for converting CO2, a secon thermal conductivity device comprising cells andresistors for creating. an electric force which is a measure of the difference in C Gz'contents of the gas in its initial condition and after the initial CO -content has been converted into CO2, and a meter for alternately measuring said electrical forces.

11. In ap aratus for gas analysis, the combination o a thermal conductivity device comprising a standard cell and a test gas cell and a resistor in each of said cells, means for converting the CO content of gas into the- CO contentv of gas'into CO2, a second thermal conductivity device 

